In the area of 1U heatsinks competition is ultra fierce. After all, an entire 1U server case is only 1.75" thick. That effectively leaves 30mm or so above the processor core for the entire thermal solution. Noise isn't much of a concern in this environment, but rather sheer cooling performance. Servers are expected to be up 99.9% of the time, and system problems due to an overheated processor is simply not going to fly.

There are essentially two
options available to heatsink manufacturers looking to penetrate this
potentially profitable marketplace. The first option is to construct a totally
passive cooling solution which takes advantage of internal drafting and fans of
a server case for air movement. These are generally the most chosen
solutions by integrators since more heatsink material can be fit on top of the
processor and nothing can break. In many instances, 1U server manufacturers
simply use stock heatsinks with their fans removed. While this cheap solution
doesn't always net the best cooling performance, it is easy for system
integrators to do.

The second option is to place
an active cooling solution on top of the processor. This is generally the more
popular choice amongst heatsink manufacturers, it is also considerably more
difficult to pull off effectively and can lead to problems if the fan stops
working, or the heatsink is badly designed.

Testing 1U
Heatsinks

This brings us to the problem
with how to test 1U heatsinks accurately, and the reason why this series of
reviews has been delayed for a while. Since the operating environment of every
1U heatsink is height limited, it would seem ideal to test these heatsinks as
such. Under this case, all 1U heatsinks would be tested with a plate
directly above the top of the cooler so that the total distance from heatsink
base to the base of this cover plate is 30mm.

Unfortunately this is where the
problems arise. Every type of heatsink, including your average desktop one is a
product of the environment to some degree. Some cases have power supplies
located directly over the processor, while other people may use socket heatsinks
on a slocket-based chip that would put sticks of memory in the direct intake
path, etc. In the case of our hard working 1U heatsinks intake fans,
drafting, orientation of heatsink relative to airflow, and countless other
factors can influence how the heatsink would perform within a specific 1U
system.

Therefore unless otherwise
noted, we will be reviewing all active heatsinks "removed from the system." The
results of our tests on 1U heatsinks will not be under height-limited system
conditions. Rather, each heatsink will be tested as if it is removed from the
system, yielding more accurate comparisons to the other heatsinks being
reviewed. The distinctions are slight, but very important for those of you
dealing with decisions on what 1U cooling solutions to consider. You at least
know the system configuration and can (and should) test your candidate heatsinks
for the particular server environment.

Passive 1U cooling solutions
will be tested with the 30mm height restriction in place and use a common
source and direction of draft air. The exact conditions of the test environment
will be described for those particular 1U heatsink reviews.

The basic design of the Arkua line of
heatsinks is quite similar, and the only real difference is whether or not they have a copper core and a big noisy fan. Since the entire body of
this 1U heatsink is 14mm thick, there isn't much room, or need for a central copper slug. It would have been interesting to see a full-copper version of the 6149, but so far we have yet to hear about one
existing.